1. Field of the Invention
This invention relates in general to variable capacity vane compressors for air conditioning systems, particularly for vehicles, and in particular to an axial pressure device that enhances sealing between a rotary valve plate and a compression housing shoulder.
2. Description of the Prior Art
One type of automotive air conditioning compressor in use is a variable capacity vane compressor. In this type of compressor, a compression housing has a chamber that is oval in shape. A cylindrical rotor extends through the chamber. The rotor has radial vanes mounted to it which slide radially in slots formed in the rotor. Refrigerant at suction pressure enters the compression chamber, with the vanes compressing the refrigerant, which passes outward through a valve.
The compressor demand varies according to speed and atmosphere conditions. At highway speed, the demand is usually lower than while idling on a hot day. To vary the capacity, a rotary valve disk or plate mounts in front of the compression housing and in engagement with a shoulder on the compression housing. The valve plate has a slotted perimeter which will change the position of the opening from the intake chamber into the compression chamber depending upon the rotational position of the valve plate. The valve plate is rotatably carried in a rotary valve housing, also known as a rear side block. The particular rotational position of the valve plate will change the quantity of refrigerant introduced between the vanes for compression by changing the timing of the compression cycle.
An actuator will rotate the valve plate to selected positions depending upon the changes in the discharge pressure and the intake or suction pressure. In one type, such as shown in U.S. Pat. No. 5,145,327, the actuator member comprises radial projections mounted to the rear side of the rotary valve plate and located within chambers. Each projection serves as a piston. Variable fluid pressure is applied to both sides of each piston. Also, a spring will urge the plate to a minimum delivery position.
A control valve supplies a control pressure to one side of each piston, the other side of each piston being at intake pressure. The control valve includes a bellows which has a stem that engages a ball valve. The bellows is located in a portion of the suction chamber. A plunger or bias pin on the opposite side of the ball has one end exposed to discharge pressure. The plunger and the stem of the bellows cooperate depending upon the discharge and intake pressure to selectively apply a control pressure to one side of the pistons for moving the rotary valve plate.
In another type of actuator, the rotary valve plate is rotated by a spool piston, such as shown in U.S. Pat. No. 4,838,740. The spool piston moves linearly transverse to the axis of the rotor. The spool piston has a pivot pin that engages the plate to cause it to rotate as the spool piston moves. Patents exist which disclose a variety of control valves for applying pressure to the spool piston to cause it to move in response to intake and discharge pressure.
Whether the actuator is a linear piston or a radial projection, the rotary valve plate slidingly engages a shoulder facing rearward on the compression housing. The shoulder surrounds the compression chamber. The valve plate slidingly engages this shoulder as the valve plate rotates. Because the valve plate forms one end of the compression chamber, it is important to have as good a sealing as possible between the rotary valve plate and the compression shoulder. In the type of rotary valve plate wherein the actuating pistons are radially oriented projections mounted to the rear side and radially oriented, variable axial pressure is applied to the rotary valve plate because the rear side of the rotary valve plate is exposed to the chambers containing control pressure for rotating the valve plate. These chambers cause a forward acting axial force to assist in sealing between the face of the valve plate and the compression shoulder.
On the other hand, in the type utilizing a linearly movable spool piston, there is no axial pressure applied to the rear side of the rotary valve plate. Consequently, there would be a tendency for leakage to occur between the rotary valve plate and the compression shoulder. If installed very tightly, leakage could be minimized, however friction might make it difficult to rotate the rotary valve plate.